A turbocharged Diesel engine system generally comprises a Diesel engine having an intake manifold and an exhaust manifold, an external air conduit for conveying fresh air from the environment into an intake line leading to an intake manifold, an exhaust line for conveying the exhaust gas from an exhaust manifold to the environment, and a turbocharger which comprises a compressor located in the intake line for compressing the air stream flowing therein, and a turbine located in the exhaust line for driving said compressor. The turbocharged Diesel engine system further comprises an intercooler, also called a charge air cooler, located in the intake line downstream the compressor, for cooling the air stream before it reaches the intake manifold, and a Diesel Oxidation Catalyst (DOC) located in the exhaust line downstream the turbine, for degrading residual hydrocarbons and carbon oxides contained in the exhaust gas. The turbocharged Diesel engine systems can also be equipped with a Diesel Particulate Filter (DPF) located in the exhaust line downstream the DOC, for capturing and removing diesel particulate matter (soot) from the exhaust gas.
In order to reduce the polluting emission, most turbocharged Diesel engine system actually comprises an exhaust gas recirculation (EGR) system, for selectively routing back exhaust gas from the exhaust manifold into the intake manifold. The exhaust gas mixed with the fresh induction air is aspired into the engine cylinders, in order to reduce the production of oxides of nitrogen (NOx) during the combustion process.
Conventional EGR systems comprise an high pressure EGR conduit for fluidly connecting the exhaust manifold with the intake manifold, an EGR cooler for cooling the exhaust gas before mixing it with the induction air, valve means for regulating the flow rate of exhaust gas through the EGR conduit, and a Electronic Control Unit (ECU) based on a microprocessor for determining the required amount of exhaust gas and for controlling said valve means accordingly. In order to further reduce the NOx emission, improved EGR systems comprise also an additional Low Pressure EGR (LPE) conduit, which fluidly connects the exhaust line downstream the DPF with the intake line upstream the compressor, an additional EGR cooler located in the additional EGR conduit, and additional valve means for regulating the flow rate of exhaust gas through the additional EGR conduit. In these improved systems, while the conventional EGR conduit defines a short route for the exhaust gas recirculation, the additional EGR conduit defines a long route for the exhaust gas recirculation, which comprises also a relevant portion of the exhaust line and a relevant portion of the intake line.
While low pressure EGR conduit systems have several benefits, as explained above, they also raise the complexity of the engine structure and give rise to a certain number of technical problems. Since these low pressure EGR conduits re-circulate exhaust gas with vapor content due to fuel combustion this causes the problem that, under certain engine operating, conditions the air path components in the portion comprising the compressor and the charge air cooler can experience a high value of relative humidity that may even lead to water condensation in the form of water droplets and therefore damage and corrosion of these components.
At least a first aim is therefore to protect the mentioned air path from damage due to an undesired high value of relative air humidity. At least a further aim is to avoid the risk of water condensation in said air path of the engine. At least another aim is to provide such protection strategy without using complex devices and taking advantage from the computational capabilities of the Electronic Control Unit (ECU) of the vehicle. In addition, other aims, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.